Electrical circuits



Dec. 27, 1927. 1,6 54,098

- T. E.'SHEA ELECTRICAL CIRCUITS Filed Feb. 27'. 1926 I! Alllll IITVIV hvenfar." iimaffiy [f Men by Affj' Patented Dec. 21,1927.

UNITED STATES TIIOTHY E. SHEA, OF RUTHERFORD,

PATENT OFFICE.

NEW JERSEY, ASSIGNOB TO WESTERN ELECTRIC COMPANY, INCORPORATED, OFJNEW YOBIL'K. Y., A CORPORATION OF NEW YORK.

uncritical. cinemas-.

This invention relates to electrical circuits. and particularly circuits consisting of resistance networks in combination with equalizers or other networks, and has for an object to improve the design of such circuits; particularly to increase the latitude of choice oi impedance elements which may be used in a network designed to have. a given transmission characteristic.

Networks consisting solely of resistance elements arranged in T or H form, are often employed toproduce a desired attenuation,

as, tor example, to prevent overloading in repeaters. Such networks are commonly reterred to as pads. In circuits employing a pad it is the practice to design the pad so that its impedances match the impedances of the circuits to which it is connected. li-lieretotore so far as known, when an equaltllt iaer network was used in such a combination it was connected to one set out terminals of the. pad and given the same impedance as the pad and circuit to which it was connected. With such an arrangement, the values tor the elements of the equalizer are hired by the transmission characteristic de sired and the impedance at the pad with which it is associated. Often, impedance elements of values thus determined cannot till be economically obtained.

In accordance with this invention the resistance pad is split and the network in serted within it, thus giving it a new. value ot impedance, equal to the impedance of the tilt pad at the split point. This method gives a considerable latitude of choice of elements tor the network since the pad can be split at a point which gives a desirable impedance.

This invention can be more readily understood by reterence to description in connection with the drawing in which". Fig.1 shows a generalized circuit of a network and T type pad connected in 4 series; Fig. 2 a specific cuit of Fig. 1,;Fig. 3 a generalized circuit of a network inserted within. a T type pad .inaccordance with this invention; 1g. 4 a

ill

the following detailed example of the cir- Application filed. February 2?, 1926." Serial. No. 91,220.

specific example of the circuit of Fig. 3;

Fig. 5 a generalized circuit of a network connected in series with a 11 type pad; Fig. 6 a specific example of thecircuit of Fig. 5; Fig. 7 a generalized circuit of a network inserted within a H type pad in accordance. with this invention; Fig. 8 a specific example of the circuit of Fig. 7 Fig. 9 a generalized circuit of another method of inserting a network within a T ty e pad; and Fig. 10 ageneralized circuit oi another method of inserting a network within a ll type pad.

Fig. 1 shows a T type pad comprising the series resistances R and R and the shunt resistance R. connected between terminals 11., l2, l8 and it.- At the terminals 13 and la the pad'is adapted to be connected to a at circuit having an impedance 5% while at the terminals 11 and l2. it is adapted to, be con nected. to an impedance 4%. 'llhe pad is therefore designed so that the impedance looking into it at theterminals 13 and 14 7c is and at the terminals 11 and His 2; Uonnected in tandem with the pad is a generaliaed attenuation correcting network of the constant resistance type described and claimed in U. S. Patent 1,603,305, issued 15 October 19, 1926 to O. J. Zobel. This network comprises the resistance R and the gen eralized impedance Z connected in parallel with one another in the series arm and a generalized impedance shunt arm. The impedance elements of 7 this network are designed to have values which give the network a required trans mission characteristic and an impedance equal to Z In Fig. 2 is shown a specific example of the circuit of Fig. 1. Here it is assumed that the impedances between which the pad 16 is required to work are Z =700w and Z =l20Ow which are representative values. 96 The arms of the pad are then given the values indicated, namely B 8970), R 344a, and R =430w in order to provide sufficient attenuation for the purpose required and, to match the impedances of the connected cir-' cuits. A transmission characteristic is as Z connected in the 80 sumed which requires that the impedance Z of the network 16 be an inductance and capacity in series and impedance Z an in ductance and capacity in parallel, both resonant'at24,100 cycles per second with this assumation, in order to give the network 16 an impedance equal to Z (lZOlho), the elements would have to be given the values indicated. It would be very uneeonomical to construct a coil having an inductance of .180 h. which is the value required for the series coil since it would be ditiicult to make the distributed capacity of such a coil of a value which would not. be of the same order of magnitude as that of the series condenser which has a capacity of only .000242 mt. This difiiculty is overcome by the circuit. of this invention illustrated in Figs. 3 and .4.

Fig. 3 shows a pad and a network arranged to be connected between two impedances Z and Z as in Fig. 1. In this case, however, the pad is split into two portions 13, 14, 17, 18, and 19, 20, 21, 22 so that the network lti may be inserted therebetw'een to give it a more desirable value of impedance. In the embodiment shown in this figure, the pad is broken by splitting the resistance 1%.. into two portions R and li -R The impedance Z, of the pad is then Z R Referring toFig. 4 it will be seen that in a circuit designed to meet the requirements of Fig. 2 the impedance of the network is reduced to 600 ohms, by splitting the pad in this way i and the values for the impedance elements are changed to those indicated, which may be more economically obtained in practice.

Fig. 9 shows a generalized circuit illustrating the method of inserting the network in a T type pad by splitting the shunt resistance R which may be desirable in some cases in order to obtain an optimum value for the network impedance.

Fig. 5 shows a circuitsimilar to that of; Fig. 1 except that in this case the pad is of the H type composed of a series resistance R and two shunt resistances B and R...

Fig. 6 shows a specific example of this type of circuit inwhich the impedances between which it is connected are 5, and

Z =12O0w as was assumed for the circuit. of Fig. 2. Assuming in this case a transmission characteristic such that the network 16 must consist of series and shunt arms resonate at 210 cycles per second, it would then be necessary to give the elements the values indicated. Condensers of capacity .24 mt. and'1.65 mt, respectively are thus obtained. Since the cost of condensers of capacity greater than 0.1 mt. varies practically directly with their size a more economical design of the network can be obtained by reducing these capacities. This can be done by the arrangement of this invention shown in Figs. 7 and 8 in which the pad is split into two portions 33, 34, 35, 36

portions, R and R and 37, 38, 39, 40. This is accomplished by splitting the shunt resistance R, into two With this arrangement the values for the. elements are as follows:

Fig. 8 shows a specific example of this type of circuit ('lesigned to meet the requirements assumed for the circuits of Fig. (i. The pad is split to insert the network at a point at which the impedance Z, is 18000). lVith this arrangement values of .16 ml. for the series condenser and 1.1 mt. tor the shunt condenser are obtained. This gives a total capacity of 1.26 ml. as compared with 1.89 mf. for the network of Fig. 6, which results in a considerable saving.

Fig. 10 shows a mmlilication oi the circuit of Fig. 7 in which a 11 type pad is split by dividing the series resistance R,,. This arrangement may be desirable in some cases in order to obtain an'opt-imumvalue for the impedance of the network.

\Vhat is claimed is:

1. In an electrical circuit having two pertions, a pair of four-terminal resistance networks included between said portions and connected respectively thereto at a pair of terminals, said net-works being proportioned to present to the circuit portions to which they are respectively connected, impedances equal to the circuit impcdances, and to have impedances at their other pairs of terminals equal to each other and ditlerent from the impedances of either of said portions and having an attenuation equivalent to that of a single resistance network of series and shunt resistance. elements so proportiom-d that. it would match the impedances ot said portions it connected alone. thcrehetweeu. and a network comprising reactive iln||cdauce elements connected between said resistance networks, said reactive. impedan e network having an impedance equal to the impedance of said resistance networks at the. terminals to which it is connected.

2. A combination according to the preceding claim in which said impedance network is a constant resistance attenuation correcting network.

- 3. A method of combining a network of impedance elements designed to give a desired transmission characteristic and to match the impedance of the circuit to which the network is connected, with a resistance net llo 1,as4,oea a work of series and shunt resistance elements, terminal, and connecting the network of so as to obtain economical values for the impedance elements within the resistance netimpedance elementsof the iietwork'which work at that point. a 10 comprises dividing the resistance network In witness whereof, I hereunto subscribe 5 into two portions at a point which willgive my name this 26th day of February A. D.

a desired im dance diflerent from the im- 1926.

pedance of t a resistance network at either TIMOTHY E. SHEA. 

